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-rw-r--r--man/systemd.exec.xml20
1 files changed, 20 insertions, 0 deletions
diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index a39e800854..dbfc7692f7 100644
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -1539,6 +1539,26 @@
<citerefentry project='man-pages'><refentrytitle>termcap</refentrytitle><manvolnum>5</manvolnum></citerefentry>.
</para></listitem>
</varlistentry>
+
+ <varlistentry>
+ <term><varname>$JOURNAL_STREAM</varname></term>
+
+ <listitem><para>If the standard output or standard error output of the executed processes are connected to the
+ journal (for example, by setting <varname>StandardError=journal</varname>) <varname>$JOURNAL_STREAM</varname>
+ contains the device and inode numbers of the connection file descriptor, formatted in decimal, separated by a
+ colon (<literal>:</literal>). This permits invoked processes to safely detect whether their standard output or
+ standard error output are connected to the journal. The device and inode numbers of the file descriptors should
+ be compared with the values set in the environment variable to determine whether the process output is still
+ connected to the journal. Note that it is generally not sufficient to only check whether
+ <varname>$JOURNAL_STREAM</varname> is set at all as services might invoke external processes replacing their
+ standard output or standard error output, without unsetting the environment variable.</para>
+
+ <para>This environment variable is primarily useful to allow services to optionally upgrade their used log
+ protocol to the native journal protocol (using
+ <citerefentry><refentrytitle>sd_journal_print</refentrytitle><manvolnum>3</manvolnum></citerefentry> and other
+ functions) if their standard output or standard error output is connected to the journal anyway, thus enabling
+ delivery of structured metadata along with logged messages.</para></listitem>
+ </varlistentry>
</variablelist>
<para>Additional variables may be configured by the following